The use of alkali developable non-amplified photoresists in the fabrication of microelectronic devices is well-known. Wet-developable systems have undergone many improvements in order to get a higher degree of integration on the semiconductor substrate.
These developments have included modification to the sensitizer which, in the case of the "conventional" diazoquinone-novolak system, serves as a dissolution inhibitor to permit certain regions (i.e., the exposed areas) of the patterned resist layer to be dissolved while maintaining the remaining region (i.e., unexposed areas) as an insoluble layer.
The light sensitive diazoquinone sensitizers have been modified to achieve sensitivity to different wavelengths. Such materials are generally described in U.S. Pat. Nos. 2,767,092, 3,050,389, 3,061,430 and 3,640,992. These materials are admixed with alkali-soluble resins or fatty acids to inhibit alkali solubility. Upon light-induced chemical reaction, the solubility of such film compositions is altered in the exposed regions to permit the formation of patterns with an aqueous developer.
Much activity has gone into developing improved sensitizers and compositions which incorporate such sensitizers. U.S. Pat. No. 4,397,937 is directed to sensitizers of improved sensitivity and solubility in novolak resins permitting higher sensitizer loading. Such compositions show increased sensitivity in the mid UV optical spectrum and to electron beam exposure.
A problem noted in optical exposure has been the fall off in contrast or line definition between areas of exposure and non-exposure. At the boundaries of such patterning there have been found regions where there is light (weak) exposure causing a gradient in the development that prevents the formation of sharp side-walled images.
U.S. Pat. No. 4,618,564 is directed to compositions comprising a film forming organic material consisting essentially of an aqueous base soluble material and a substance which releases sulfonic acid upon exposure to active radiation to make the exposed regions of the film more soluble to aqueous base developers. The sulfonic acid releasing materials include sulfonate esters and aromatic N-sulfonyloxyimides. These materials can be flood exposed after patterning and substrate processing to make the remaining patterned layer soluble in aqueous base developer.
Patent application, U.S. Ser. No. 322,848, filed Mar. 14, 1989, the disclosure of which is incorporated by reference into the present application, discloses chemically amplified photoresist compositions having a polymeric or molecular composition whose solubility is dependent upon the presence of acid removable protecting groups and a sulfonic acid precursor which generates a strong acid upon exposure to radiation. The preferred sulfonic acid generators are sulfonyloxyimides of the form ##STR1## where C.sub.1 and C.sub.2 may form a single or double bond wherein R is selected from --(CH.sub.2).sub.n --Z and --(CF.sub.2).sub.n --Z where n=0 to 4, where Z is H,F, alkylaryl ##STR2## where m is from 1 to 5, provided that when Z is H,F or alkylaryl n must be at least 1, and where X and Y (1) form a cyclic or polycyclic ring which may contain one or more hetero atoms, (2) form a fused aromatic ring, (3) may be independently H, alkyl or aryl, (4) may be attached to another sulfonyloxyimide containing residue, or (5) may be attached to a polymeric chain or backbone.
A preferred sensitizer described for use in deep UV chemically amplified resist systems is trifluoromethylsulfonyloxybicyclo[2.2.1]-hept-5-ene-2,3-dicarboximide (MDT) and having the structure ##STR3##